The present invention relates to temperature sensors, and in particular to a temperature sensor capable of operating in high vibration environments with improved accuracy and a high temperature range.
The temperature of a process fluid in an industrial process is typically measured by a temperature sensor or probe that is positioned in the fluid. The temperature sensor may use a thermocouple or a resistance temperature detector (RTD) to produce an electrical signal that is a function of temperature.
A thermocouple makes use of two dissimilar metals with different Seebeck coefficients. The thermocouple generates a voltage based upon a temperature difference between the thermocouple junction and a reference junction. The thermocouple offers a wide temperature operating range (typically from 0° C. to 1450° C.), and does not require a power source to generate an output signal. Thermocouples also are capable of operating in high vibration environments. However, thermocouples are less accurate than RTD devices.
A resistance temperature detector (RTD) senses temperature by a change in electrical resistance of a metal. The higher the temperature of the RTD, the higher the resistance. An output signal of the RTD sensor is generated by passing a constant electrical current through the RTD and measuring the voltage produced.
An RTD may be either a wire wound or a thin film device. The RTD may be encapsulated in a temperature probe and used in conjunction with an industrial process transmitter to generate a transmitter output representing the temperature of the fluid in contact with the probe. Platinum is commonly used in wire wound and thin film RTDs, and provides stable and accurate measurement of temperatures up to about 600° C. to 650° C.
When compared to thermocouples, RTD devices are capable of higher accuracy but have smaller overall temperature range. Also, RTD devices are more susceptible to damage or failure in high vibration environments than are thermocouples.
There is a need for a temperature sensor capable of operation in high vibration environments with the accuracy of an RTD and with a better high temperature range than is currently available with RTDs designed for high vibration environments.